The...science? of time travel

Time travel. Time travel. Science blog, time travel. Okay. Right. Let’s do this thing.

We can’t do time travel. Time is a strange thing which is hard to get a handle on, and the best definition I have come across of it is John Wheeler’s, who said “Time is what prevents everything from happening at once”. And it only points one way.

So that’s that.

Hmm?

You want more than that?

Oh alright then, let’s talk about a weird idea. It’s not time travel like we here at AST depict, but it’s…well, let’s not get ahead of ourselves.

Let’s start here: This is the Dirac Equation.

It’s one of my favourites.

It was Dirac’s greatest work – an equation which combined quantum theory and relativity to fully describe the properties of certain types of tiiiiiny particles, like electrons. It’s actually four intricately connected equations and it describes the possible states your electron could be in.

So the equation, when you work through it, gives you four different solutions. Which is all fine and dandy – two of the solutions correspond beautifully, and help to explain, some experimental results which had been causing some headaches at the time. The trouble was with the other two solutions – they describe a situation where you could end up with an electron which has negative energy.

Negative, as in less than zero.

How could you have less than zero energy?

Now usually in physics this wouldn’t be a problem – when you get weird stuff like that it’s perfectly valid to say “Well, that’s a bit unphysical, so let’s ignore it”. But you can’t do that in quantum physics. Oh no. In quantum physics there is a saying: That which is not forbidden is mandatory. so if a solution gives you negative energy, that means there is a certain probability that this will take place – it might be a small probability, but it’s a big universe, so it must have happened somewhere.

But Dirac believed in his equation. So he said, okay well then there must be these funny things which are the opposite to electrons. Electrons with a goatee, you might say. Sounds weird, but that’s what the equations tell us. Trust in the equations. These particles are out there.

And then they found one.

 

The curved track is a positron

The curved track is a positron

It is identical to an electron, except it has a positive charge. It’s called a positron, and it’s an antiparticle. If a positron and an electron meet, then cancel each other out and produce a photon – this is, in fact, how PET scanners work (the P stands for Positron). We now have a reasonable handle on positrons, we’ve even managed to work out that a standard banana will produce one positron every 75 minutes. So there’s that.

How does this tie in with time travel? Well, let us say hello to Richard Feynman.

He was a physicist, a brilliant, mad one. His memoirs are well worth reading.

And he suggested that a positron is actually an electron which is moving backwards in time.

So when an electron and positron collide and interact, that is an electron changing direction in time.

And John wheeler, who I quoted above, went even further and suggested that, in fact, there is only one electron and it just has a very complicated timeline – moving forwards and backwards, interacting with itself.

Mathematically this approach produces results which are quivalent to other, less mind-bending, views of how it all works. So who knows, maybe that is what’s happening?

I suspect, however, that the Time Artist doesn’t spend much of his time thinking about positrons. Or science. Or the consequences of his actions. Or anything much, really…

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2 thoughts on The...science? of time travel

    • Action Dan

      Boom! Action Science Theatre, closer to truth than fiction (obviously)…

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